Skilled use of the hands is impaired in a variety of neurological diseases, such as strokes, Parkinson's disease, and peripheral neuropathies, as well as by diseases affecting the musculoskeletal system, such as arthritis. An understanding of the normal patterns of coordination of wrist and finger movements is a prerequisite for an understanding of the physiopathology of these disease states as well as rehabilitative efforts. The long term goal of this project is to arrive at a better understanding of how the nervous system controls the large number of degrees of freedom of the hand by studying normal kinematics and kinetics of human finger movements. The present proposal has two specific aims: 1) the characterization of the precision grip under circumstances when two or more fingers are coordinated with the thumb to grasp an object and 2) the study of sequences of skilled finger movements (typing, piano playing) in order to better understand how skilled movements may be generated by assembling simpler elements. The proposed studies of the precision grip are based on the hypothesis that this task involves postural synergies comprising two or more fingers and that there are neural constraints that limit the extent to which the motion and/or the force generated by each finger can be controlled independently. In particular, we will determine the extent to which the direction of force exerted by each finger can be controlled individually, the extent to which such finger contact forces depend on the geometric details of the object to be grasped and the extent to which the posture of the hand prior to contact is adapted to the object's geometry. Psychophysical studies designed to uncover the nature of the sensorimotor transformations between visual and proprioceptive information about hand posture are also proposed. These studies are based on the hypothesis, supported by previous work, that the neural implementation of geometrically nonlinear transformations may involve substantial approximations, leading to errors in movement and posture. The proposed study of piano playing will test the generality of the phenomenon of strictly serial sequencing of movements observed during typing. Hand and finger kinematics and contact forces will be measured using a variety of video and electronic devices.